Advances in field emission display technology are disclosed in U.S. Pat. No. 3,755,704, "Field Emission Cathode Structures and Devices Utilizing Such Structures," issued 28 Aug. 1973, to C. A. Spindt et al.; U.S. Pat. No. 4,857,799, "Matrix-Addressed Flat Panel Display," issued 15 Aug. 1989, to C. A. Spindt et al.; U.S. Pat. No. 4,940,916, "Electron Source with Micropoint Emissive Cathodes and Display Means by Cathodoluminescence Excited by Field Emission Using Said Source," issued 10 Jul. 1990 to Michel Borel et al.; U.S. Pat. No. 5,194,780, "Electron Source with Microtip Emissive Cathodes," issued 16 Mar. 1993 to Robert Meyer; and U.S. Pat. No. 5,225,820, "Microtip Trichromatic Fluorescent Screen," issued 6 Jul. 1993, to Jean-Frederic Clerc. These patents are incorporated by reference into the present application.
The Clerc ('820) patent discloses a trichromatic field emission flat panel display having a first substrate, on which are arranged a matrix of conductors. The first substrate is also called the cathode plate or the emitter plate. In one direction of the matrix, conductive columns comprising the cathode electrode support the microtips. In the other direction, above the column conductors, are perforated conductive rows comprising the grid electrode. The row and column conductors are separated by an insulating layer having apertures permitting the passage of the microtips, each intersection of a row and column corresponding to a pixel.
On a second substrate, facing the first, the display has regularly spaced, parallel conductive stripes comprising the anode electrode. The second substrate is also called the anode plate. These stripes are alternately covered by a first material luminescing in the red, a second material luminescing in the green, and a third material luminescing in the blue, the conductive stripes covered by the same luminescent material being electrically interconnected.
The Clerc patent discloses a process for addressing a trichromatic field emission flat panel display. The process consists of successively raising each set of interconnected anode stripes periodically to a first potential which is sufficient to attract the electrons emitted by the microtips of the cathode conductors corresponding to the pixels which are to be illuminated in the color of the selected anode stripes. Those anode stripes which are not being selected are set to a potential such that the electrons emitted by the microtips are repelled or have an energy level below the threshold cathodoluminescence energy level of the luminescent materials covering those unselected anodes.
Luminescence is a characteristic nonthermal emission of electromagnetic radiation by a material upon some form of excitation. Thus, luminescence is the conversion of energy into light without heat. The luminescence type is usually defined by the excitation means. For example, cathodoluminance is where the source of energy is cathode rays. The luminescence process itself involves (1) the absorption of energy; (2) excitation; and (3) the emission of energy, usually in the form of radiation in the visible portion of the spectrum, however, the emission can also be in the infrared or ultraviolet portions of the spectrum. Visible light constitutes one part of the electro-magnetic spectrum (approximately 4,000 .ANG.-8,000 .ANG.).
When the luminance persists after the excitation is removed it is called phosphorescence. Quantitatively, phosphorescence may be defined as luminescence that is delayed by more than 10.sup.-8 seconds after excitation. An inorganic luminescent material, such as phosphor, usually consists of a crystalline host lattice to which is added a trace of impurities, called the activator and co-activator. The activator is usually present in concentration levels varying from a few parts per million to one or two percent of the host lattice. Co-activators are the additional impurities which act as charge compensators or donors in the lattice.
Luminous efficiency is defined as the ratio of the total luminous flux in lumens emitted by a light source over all wavelengths to the total incident energy in watts (current.times.volts). The value for lumens is adjusted to take into account the efficiency of the human eye.
It is well known that most of the commonly used flat panel display phosphors have a lower luminance efficiency at the acceleration voltage levels of the typical field emission device (below 1 kV) compared to other systems such as the Cathode Ray Tube (CRT) (25-30 kV). It is advantageous to operate the field emission device at the lower voltages because the low voltage operation simplifies spacer technology, reduces driver and interconnect cost, reduces display mortality caused by high voltage arcing, and allows the use of the switched anode design. Therefore, one shortcoming of field emission displays of the current technology is the reduced phosphor efficiency caused by the relatively low accelerating voltage between the cathode and anode plates. An improved luminance efficiency would facilitate improved display luminance and reduced power consumption.
In view of the above, it is clear that there exists a need for improved phosphor efficiency for field emission devices. More specifically, what is needed is an improvement in the method of manufacturing the anode plate of a field emission flat panel display device which facilitates improved phosphor efficiency and higher luminance.